Reference is also made to commonly-owned copending 09/442,025, filed Nov. 17, 1999; Ser. No. 09/451,344, filed Nov. 30, 1999; Ser. No. 09/663,788, filed Sep. 18, 2000; and Ser. No. 09/663,948, filed Sep. 18, 2000. The entire disclosures of each of the foregoing four (4) applications to the extent not in conflict with the present application, are incorporated herein by reference. Reference is also made to commonly-owned copending Application Ser. Nos. 09/296,499, filed Apr. 22, 1999; and Ser. No. 09/658,839, filed Sep. 8, 2000.
All of the applications referred to above relate to aqueous biocidal bromine solutions and/or their preparation or use.
Bromine-based biocides have proven biocidal advantages over chlorination-dechlorination for the microbiological control of cooling waters and disinfection of waste treatment systems. The water treatment industry recognizes these advantages to be cost-effective control at higher pH values, almost no loss in biocidal activity in the presence of ammonia, and effective control of bacteria, algae and mollusks.
A common way of introducing bromine-based biocides into a water system is through the use of aqueous NaBr in conjunction with NaOCI bleach. The user feeds both materials to a common point whereupon the NaOCl oxidizes the bromide ion to HOBr/OBrxe2x8ax96. This activated solution is then introduced directly into the water system to be treated. The feeding of the two liquids in this fashion is necessary because the HOBr/OBrxe2x8ax96 mixture is unstable and has to be generated on-site just prior to its introduction to the water. Furthermore, the feeding, and metering of two liquids is cumbersome, especially as the system has to be designed to allow time for the activation of bromide ion to occur. Consequently many biocide users have expressed the need for a single-feed, bromine-based biocide. Elemental bromine and molecular bromine chloride have been considered to meet these demands. Both are liquids at room temperature and can be fed directly to the water system, where immediate hydrolysis occurs to yield HOBr.
Br2+H2Oxe2x86x92HOBr+HBrxe2x80x83xe2x80x83(1)
BrCl+H2Oxe2x86x92HOBr+HClxe2x80x83xe2x80x83(2)
Properties of bromine and bromine chloride are compared in Table 1.
It can be seen that certain characteristics of these materialsxe2x80x94especially their corrosiveness, high vapor pressures and fuming tendenciesxe2x80x94necessitate care and skill in their handling and use. Early efforts to overcome the deficiencies of these materials comprised complexing bromine with excess bromide ion in the presence of strong acid and stabilizing the resultant solutions with ethanolamine. The resultant solutions of ethanolammonium hydrogen perbromide contained up to 38% by weight elemental bromine. See in this connection, Favstritsky, U.S. Pat. No. 4,886,915; and Favstritsky, Hein, and Squires, U.S. Pat. No. 4,966,716.
These solutions permitted introduction of bromine to a water system using a single feed. As in the case of bromine and bromine chloride, the ethanolammonium hydrogen perbromide hydrolyzed in water to release HOBr. The vapor pressures of these solutions were lower than elemental bromine and bromine chloride. Nevertheless, the solutions still possessed measurable vapor pressures, and thus tended to produce undesirable reddish-colored vapors during storage and use.
An economically acceptable way of stabilizing high concentrations of aqueous solutions of bromine chloride is described in U.S. Pat. No. 5,141,652 to Moore, et al. The solution is prepared from bromine chloride, water and a halide salt or hydrohalic acid. These solutions were found to decompose at a rate of less than 30% per year and in cases of high halide salt concentration, less than 5% per year. Moreover, solutions containing the equivalent of 15% elemental bromine could be prepared. Unfortunately, the relatively high acidity of these solutions and their tendency to be corrosive and fuming impose limitations on their commercial acceptance.
Many solid bromine derivatives such as BCDMH (N,N-bromochloro-5,5-dimethylhydantoin) are limited in the amount of material that can be dissolved in water and fed as a liquid to the water treatment system. For example, the solubility of BCDMH in water is only around 0.15%. Another limitation of such derivatives is that at neutral pH, HOBr rapidly decomposes, eventually forming bromide ions. Thus, the ability to store and transport these aqueous solutions is greatly limited and of questionable commercial feasibility.
U.S. Pat. No. 3,558,503 to Goodenough et al. describes certain aqueous bromine solutions stabilized with various stabilizing agents and various uses to which such solutions can be put. The compositions described in the patent comprise an aqueous bromine solution having from about 0.01 to about 100,000 parts per million by weight of bromine values wherein the molar ratio of bromine to nitrogen present in the bromine stabilizer ranges from about 2.0 to 1 to about 0.5 to 1. The stabilizer used is biuret, succinimide, urea, a lower aliphatic mono- or disubstituted urea containing from about 2 to about 4 carbon atoms in each substituent group, sulfamic acid, or an alkyl sulfonamide of the formula RSO3NH2 where R is a methyl or ethyl group. The solution also contains sufficient hydroxide additive to provide a pH in the solution ranging from about 8 to about 10, the hydroxide additive being an alkaline earth hydroxide or an alkali metal hydroxide.
U.S. Pat. No. 5,683,654 to Dalhnier et al. discusses the preparation of aqueous alkali metal or alkaline earth metal hypobromite solutions by mixing an aqueous solution of alkali or alkaline earth metal hypochlorite with a water soluble bromide ion source to form a solution of unstabilized alkali or alkaline earth metal hypochlorite. To this solution is added an aqueous solution of an alkali metal sulfamate having a temperature of at least 50xc2x0 C. and in an amount that provides a molar ratio of alkali metal sulfamate to alkali or alkaline earth metal hypobromite of from about 0.5 to about 6 whereby a stabilized aqueous alkali or alkaline earth metal hypobromite solution is formed. The Dallmier et al. patent teaches that much higher levels of available halogen for disinfection were attained by this approach as compared to the Goodenough et al. approach. But the Dallmier et al. patent acknowledges that in their process, the stabilization must occur quickly after the unstable NaOBr is formed.
U.S. Pat. No. 5,795,487 to Dallmier et al. describes amethod for preparing a stabilized alkali or alkaline earth metal hypobromite solution. The method comprises mixing an aqueous solution of alkali or alkaline earth metal hypochlorite having about 5-70% of available halogen as chlorine with a water-soluble bromide ion source, allowing the bromide ion source and the hypochlorite to react to form a 0.5-70 wt % aqueous solution ofunstabilized alkali or alkaline earth metal hypobromite, adding to this unstabilized solution an aqueous solution of an alkali metal sulfamate in amount to provide a molar ratio of alkali metal sulfamate to alkali or alkaline earth metal hypobromite of from about 0.5 to about 0.7, and recovering a stabilized aqueous alkali or alkaline earth metal hypobromite solution. The order of addition in the process is said to be critical.
U.S. Pat. No. 6,007,726 to Yang et al. describes the formation of stabilized bromine formulations. In that process, a solution of alkali or alkaline earth metal bromide and an halogen stabilizer such as sulfamic acid is formed and adjusted to a pH of about 4 to about 8. To this solution is added ozone, a peroxide, or a peracid such as peracetic acid, to generate an oxidizing bromine compound in the solution. The pH of the solution can then be raised to 13 or above. The process is demonstrated by use of ozone from an ozonator, and it is indicated that it is important to maintain a high reaction pH and a low reaction temperature to keep the stable oxidizing bromines from thermally decomposing.
Improved process technology for forming concentrated aqueous solutions of biocidally active bromine, and improved concentrated aqueous solutions of biocidally active bromine, are provided by this invention.
This invention involves, inter alia, the discovery that when producing concentrated aqueous solutions of biocidally active bromine in which sulfamate is present in the reaction mixture, suitable control of pH of the aqueous reaction mixture throughout the production process can have important beneficial effects upon both the reaction itself and the biocidally-active product being produced. For example, when producing a concentrated liquid biocide composition by mixing (a) bromine chloride, or bromine and chlorine with (b) an aqueous solution containing sulfamate anion, a substantial portion of the sulfamate can be hydrolyzed rather rapidly to sulfate under acidic conditions. Although the reaction mixture is sufficiently stable to produce a concentrated aqueous biocidal solution, loss of sulfamate due to hydrolysis to sulfate during the production process can result in decreased storage stability of the finished product even though sufficient base is introduced into the solution as the last step of the production process to raise the pH of the solution to 13 or above. Moreover, loss of sulfamate imposes an economic burden on the operation. On the other hand, use ofhighly basic reaction conditions throughout the production process can result in degradation of glass-lined reactors which are desirably employed to minimize the possibility of heavy metal extraction from metallic reactor surfaces, a possibility which is to be avoided since the biocidal solutions are primarily used in water treatment. Accordingly, pursuant to this invention the foregoing difficulties are minimized, if not eliminated.
Moreover, this invention enables economical production on an industrial scale of storage-stable aqueous concentrates which, because of the manner in which they are produced, can provide especially effective control of bacteria, algae, mollusks, and biomass.
Accordingly, pursuant to one of the embodiments of this invention there is provided a process of producing a concentrated liquid biocide composition, which process comprises:
A) bringing together in any feasible manner to form a reaction mixture (a) bromine atoms and chlorine atoms in the form of one or more of (i) bromine chloride, (ii) elemental bromine, and (iii) elemental chlorine, (b) a source of sulfamate anions, preferably an alkali metal sulfamate, and more preferably sodium sulfamate, (c) alkali metal base, preferably a sodium base, and most preferably sodium hydroxide and/or sodium oxide, and (d) water, such that the numerical ratio of bromine atoms to chlorine atoms brought to the mixture is in the range of about 0.7:1 to about 1.7:1, and preferably in the range of about 1:1 to about 1.2: 1; and
B) providing before and/or during A) enough alkali metal base in the mixture being formed in A) to keep the pH of such mixture in the range of about 7 to about 11, and preferably in the range of about 8 to about 10, during all or substantially all of the time the conduct of A) is occurring, the amounts of (a), (b), (c), and (d) used being amounts that form an active-bromine-containing solution in which (i) the active bromine content is at least about 50,000 ppm (wt/wt) (i.e., at least about 5 wt % of the mixture is active bromine content), and preferably at least about 100,000 ppm (wt/wt), and more preferably at least about 120,000 ppm (wt/wt), and (ii) the atom ratio ofnitrogen to active bromine originating from (a) and (b) is greater than about 0.93, and preferably greater than 1; and wherein if any sulfate is present in the active-bromine-containing solution as formed, such sulfate content is such that the molar ratio of sulfate to sulfamate in the solution is less than about 0.2, and preferably less than about 0.05.
As used anywhere in this document, including the claims, the phrase xe2x80x9cbringing together in any feasible mannerxe2x80x9d denotes that (a), (b), (c), and (d) can be brought together in any chemically feasible way of feeding, and that (a), (b), (c), and (d) can be brought together as individual entities and/or as one or more chemically feasible subcombination(s) of two or more of them. As any chemist or chemical engineer can readily understand, there are a considerable number of feasible ways of bringing (a), (b), (c), and (d) together in a chemically feasible way so that there is no splattering, excessive heat generation, or violent reaction when they are brought together. Suffice it to say here, that ordinary common sense from a chemical standpoint is expected to be observed both in interpreting this phrase and in implementing this phrase.
A preferred embodiment of this invention is a process of producing a concentrated liquid biocide composition, which process comprises:
A) feeding (a) bromine atoms and chlorine atoms in the form of one or more of (i) bromine chloride, (ii) elemental bromine, and (iii) elemental chlorine into (b) water containing sulfamate anions, or feeding each of(a) and (b) into a reaction vessel, such that the numerical ratio of the total number of bromine atoms fed to the total number of chlorine atoms fed is in the range of about 0.7:1 to about 1.7:1, and preferably in the range ofabout 1:1 to about 1.2:1; and
B) providing before and/or during A) enough alkali metal base in the mixture being formed in A) to keep the pH of such mixture in the range of about 7 to about 11, and preferably in the range of about 8 to about 10, during all or substantially all of the time feeding in A) is occurring, the amounts of(a), (b), (c), and (d) used being amounts that form an active-bromine-containing solution in which (i) the active bromine content is at least about 50,000 ppm (wt/wt), and preferably at least about 100,000 ppm (wt/wt), and more preferably at least about 120,000 ppm (wt/wt), and (ii) the atom ratio of nitrogen to active bromine originating from (a) and (b) is greater than about 0.93, and preferably greater than 1; and wherein if any sulfate is present in the active-bromine-containing solution as formed, such sulfate content is such that the molar ratio of sulfate to sulfamate in the solution is less than about 0.2, and preferably less than about 0.05.
Preferably, after completing of the feeding in A) in the above processes, the pH of the active-bromine-containing solution is raised to at least about 12, and more preferably to a pH that is at least in the range of about 13 to about 13.5. Typically this is accomplished by adding additional alkali metal base to, or otherwise mixing additional alkali metal base with, the active-bromine-containing solution.
Another embodiment of this invention is a process of minimizing or eliminating loss of sulfamate during production of a sulfamate-stabilized liquid biocide composition, which process comprises:
A) feeding (a) bromine atoms and chlorine atoms in the form of one or more of (i) bromine chloride, (ii) elemental bromine, and (iii) elemental chlorine into (b) water containing sulfamate anion, or feeding each of (a) and (b) separately into a reaction vessel, or otherwise bringing (a) and the components of (b) together by feeding them in any way except feeding any of the components of (b) singly or in any combination into (a), and
B) minimizing sulfate formation in the resultant aqueous solution by providing before and/or during A) enough alkali metal base in the mixture being formed in A) to keep the pH of the mixture in the range of about 7 to about 11, and preferably in the range of about 8 to about 10, during all or substantially all of the time the feeding of A) is occurring so that loss of sulfamate is minimized or eliminated. Thus if any sulfate is formed and is present, the molar ratio of sulfate to sulfamate in the concentrated liquid biocide composition as formed is typically less than about 0.2, and preferably less than about 0.05.
In conducting this embodiment it is preferred, but not essential, to proportion (a) and (b) such that numerical ratio of the total number of bromine atoms fed to the total number of chlorine atoms fed is in the range of about 0.7:1 to about 1.7:1, and preferably in the range of about 1:1 to about 1.2:1. Also, in conducting this embodiment it is preferred, but not essential, to use (a) and (b) in amounts that form an active-bromine-containing solution in which (i) the active bromine content is at least about 50,000 ppm (wt/wt), and preferably at least about 100,000 ppm (wt/wt), and more preferably at least about 120,000 ppm (wt/wt), and (ii) the atom ratio of nitrogen to active bromine originating from (a) and (b) is greater than about 0.93, and preferably greater than 1. In addition, it is preferable when conducting this embodiment to raise the pH of the aqueous solution after completing the feeding of A), to at least about 12, and more preferably to a pH that is at least in the range of about 13 to about 13.5.
As will be described more fully hereinafter, there are various ways by which the bromine atoms and chlorine atoms of (a) can be fed using members of the group consisting of bromine chloride, bromine and chlorine. For example, some of the preferred ways involve feeding (1) bromine chloride by itself, (2) bromine chloride in a mixture with bromine, or (3) bromine and chlorine fed separately and concurrently and/or fed separately and sequentially with either one being fed first.
In all of the embodiments of this invention described above, the feeds in A) can be conducted in any manner as long as the pH of the mixture being formed stays or is kept in the range of about 7 to about 11, and preferably in the range of about 8 to about 10, during all or substantially all of the time feeding in A) is occurring. For example, the feed of (a) into (b) can be continuous or intermittent, or both. Likewise the separate feeds of (a) and (b) into a reaction vessel can be continuous or intermittent, or both, and these separate feeds are concurrent or substantially concurrent feeds, and/or these separate feeds are conducted in alternating sequences. To keep the pH in the range of about 7 to about 11, and preferably in the range of about 8 to about 10, during all or substantially all of the time feeding in A) is occuring:
1) dissolved alkali metal base can be included in (b) and/or
2) a water solution of alkali metal base can be separately fed, continuously or intermittently, or both, either (i) as a feed into (b), or (ii) as a feed along with separate feeds of (a) and (b) into a reaction vessel, whichever of (i) and (ii) is being carried out in A).
In preferred embodiments, the sulfamate anion of (b) is provided by mixing together in water, (i) sulfarnic acid and/or an alkali metal salt of sulfamic acid, and (ii) alkali metal base in proportions such that an aqueous solution of alkali metal salt of sulfamic acid is formed having a pH of at least 7 and preferably at least 8. If sulfamic acid itself is used as the starting material, it is used initially as a slurry in water with which the alkali metal base is mixed.
Operation in accordance with the above embodiments ofthis invention not only results in minimized hydrolysis of sulfamate to sulfate, but aqueous biocidal solutions produced in this manner when used in proper dosage levels provide especially effective control of bacteria, algae, mollusks, and biomass. Also, if the reaction of (a) with (b) is carried out in a glass-lined reaction vessel, the glass lining will not undergo as severe attack as it would ifthis entire reaction were conducted at a higher pH such as 12, 13 or 14.
Still another embodiment of this invention is a process producing a liquid biocide composition wherein the pH of the reaction mixture is controlled in at least three stages. The process of this embodiment comprises:
I) bringing together in any feasible manner to form a reaction mixture (a) bromine atoms and chlorine atoms in the form of one or more of (i) bromine chloride, (ii) elemental bromine, and (iii) elemental chlorine, (b) a source of sulfamate anions, preferably an alkali metal sulfamate, and more preferably sodium sulfamate, (c) alkali metal base, preferably a sodium base, and most preferably sodium hydroxide and/or sodium oxide, and (d) water, such that (1) the numerical ratio of bromine atoms to chlorine atoms brought into the mixture is in the range of about 0.7:1 to about 1.7:1, and preferably in the range of about 1:1 to about 1.2:1, and (2) the atom ratio of nitrogen to active bromine originating from (a) and (b) is greater than about 0.93, and preferably greater than about 1; to form an active-bromine-containing reaction product mixture that has, initially, a pH over 11, preferably at least about 12, and more preferably at least about 13;
II) providing before and/or during the conduct of I) an amount of alkali metal base in relation to the total amount of acid (HBr and/or HCl) co-product(s) to be formed in the reaction, that results in the pH of such reaction product mixture decreasing by at least 1 pH unit during the conduct of I), to a pH in the range of about 7 to about 11, and preferably to a pH in the range of about 8 to about 10;
III) keeping the reaction mixture at a pH in the range of about 7 to about 11, and preferably at a pH in the range of about 8 to about 10 for a period of time that increases the microbiocidal effectiveness of the concentrated liquid biocide composition being formed; and then
IV) raising the pH of the resultant active-bromine-containing reaction product mixture to at least about 12, and preferably to a pH that is at least in the range of about 13 to about 13.5, by mixing additional alkali metal base therewith.
Among feasible ways of bringing (a), (b), (c), and (d) together per I) above are operations wherein (b), (c), and (d) are brought to the reaction mixture by feeding (b), (c), and (d) as individual entities and/or by feeding any two or all three of (b), (c) and (d) as one or more preformed mixtures of such any two or all three thereof, and operations wherein (a), (b), (c), and (d) are brought together in any chemically feasible manner of feeding. Typically, neither (b), nor (c), nor (d), singly or in any combination(s) or sub-combination(s) with each other, would be fed into (a),
Yet another embodiment of this invention wherein the pH of the reaction mixture is controlled in at least three stages is a process of producing a concentrated liquid biocide composition, which process comprises:
I) feeding (a) bromine atoms and chlorine atoms in the form of one or more of (i) bromine chloride, (ii) elemental bromine, and (iii) elemental chlorine, into (b) an aqueous solution of sulfamate anions and alkali metal base, or feeding each of (a) and (b) into a reaction vessel, such that the numerical ratio of bromine atoms to chlorine atoms fed is in the range of about 0.7:1 to about 1.7:1, and preferably in the range of about 1:1 to about 1.2:1, to form an active-bromine-containing reaction product mixture that has, initially, a pH over 11, preferably at least about 12, and more preferably at least about 13;
II) providing before and/or during the feeding in I) an amount of alkali metal base in relation to the total amount of acid (HBr and/or HCl) co-product(s) to be formed in the reaction, that results in the pH of such reaction product mixture decreasing by at least 1 pH unit during the feeding in I), to a pH in the range of about 7 to about 11, and preferably to a pH in the range of about 8 to about 10;
III) keeping the reaction product mixture at a pH in the range of about 7 to about 11, and preferably at a pH in the range of about 8 to about 10, for a period of time that increases the microbiocidal effectiveness of the concentrated liquid biocide composition being produced; and then
IV) raising the pH of the resultant active-bromine-containing reaction product mixture to at least about 12, and preferably to a pH that is at least in the range of about 13 to about 13.5, by mixing additional alkali metal base therewith.
Instead ofperforming II) as specified above, the decrease in pH pursuant to II) in each of the above processes can occur after completing the feeding in I) by using enough base to keep the pH over 11, preferably at least about 12, and more preferably at least about 13 during the feeding, and by adding to the resultant reaction mixture after completing the feeding in I), enough HBr and/or HCl to cause the pH to decrease as specified in II) above. However this is a less preferred way of operating.
If desired, operation pursuant to IV) in each of the above processes can be conducted in two or more stages of increased pH levels. However, preferably the pH is adjusted to the desired final pH value in a one-stage operation.
In each of the embodiments of this invention, the atom ratio of nitrogen based on sulfamic acid (plus alkali metal base) or alkali metal sulfamate used to active bromine is preferably greater than 1, and more preferably in the range of about 1.1 to about 1.5. Still higher ratios can be employed, if desired.
The above and other embodiments ofthis invention will be still further apparent from the ensuing description and appended claims.